I am fairly certain that your car will not drop to 8 capacity bars by the end of 2019, but you should have at least 60 miles of usable range (highway driving with normal A/C use) in the summer and 50 miles (with reasonable heating) during winter.
That estimate is a bit high. I'm guessing that most of your driving is on flat terrain? I still have 12 bars showing, and have barely 50 miles of Winter range right now. In frigid weather it's more like 38-40 miles, again with 12 bars and about 86% SOH.